全文获取类型
收费全文 | 2494篇 |
免费 | 251篇 |
国内免费 | 240篇 |
专业分类
林业 | 74篇 |
农学 | 187篇 |
基础科学 | 20篇 |
276篇 | |
综合类 | 925篇 |
农作物 | 251篇 |
水产渔业 | 280篇 |
畜牧兽医 | 444篇 |
园艺 | 77篇 |
植物保护 | 451篇 |
出版年
2024年 | 22篇 |
2023年 | 71篇 |
2022年 | 121篇 |
2021年 | 143篇 |
2020年 | 143篇 |
2019年 | 137篇 |
2018年 | 112篇 |
2017年 | 127篇 |
2016年 | 149篇 |
2015年 | 134篇 |
2014年 | 142篇 |
2013年 | 142篇 |
2012年 | 150篇 |
2011年 | 152篇 |
2010年 | 114篇 |
2009年 | 98篇 |
2008年 | 112篇 |
2007年 | 104篇 |
2006年 | 108篇 |
2005年 | 81篇 |
2004年 | 66篇 |
2003年 | 66篇 |
2002年 | 64篇 |
2001年 | 58篇 |
2000年 | 51篇 |
1999年 | 37篇 |
1998年 | 37篇 |
1997年 | 24篇 |
1996年 | 25篇 |
1995年 | 37篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 26篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1963年 | 1篇 |
1956年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有2985条查询结果,搜索用时 234 毫秒
131.
很多藻类致病菌具有广谱溶藻活性。本研究发现紫菜黄斑病致病菌地中海弧菌Vibrio mediterranei 117-T6(Vm 117-T6)对赤潮异湾藻、颗石藻、叉编金藻和东海原甲藻等微藻也具有较强的溶藻活性,可使其叶绿素含量显著降低,是一株广谱性溶藻细菌。Vm 117-T6能在40 min内使赤潮异弯藻的活动能力下降,光合作用受抑,感染120 min即可导致藻体裂解并产生白色絮状沉淀。Vm 117-T6能降解卡拉胶,不能降解果胶、纤维素和几丁质。菌体、胞内及胞外提取物均具有较强的溶藻活性,其胞外溶藻物质易溶于水、不溶于石油醚和乙酸乙酯,具较强极性;耐高温、不易被活性炭吸附、乙醇处理会降低溶藻活性。Vm 117-T6在常规与易感条件下的关键差异蛋白包括大量的ABC转运蛋白、外膜蛋白、鞭毛蛋白及少量Toxin。这些研究结果提示Vm 117-T6毒力效应物中含有极性非蛋白质类物质,且与毒力因子转运、分泌以及细胞黏附相关的蛋白可能在其毒力作用中发挥重要作用。上述研究结果表明:多种溶藻机制参与了Vm 117-T6的溶藻过程。 相似文献
132.
应用细菌质粒转化技术,将大肠杆菌K_(?)与LT(A~-B~ )抗原基因重组质粒转入猪霍乱沙门氏菌弱毒菌苗株中.对获得的其中8个转化子进行鉴定的结果表明,转化的细菌仍保持沙门氏菌的形态、生化及抗原特性,同时可稳定地表达K(?)和LT-B两种抗原.用微量间接血凝试验、抗甘露糖豚鼠红细胞凝集试验(MRHA)、ELISA等对转化菌表达的K(?)抗原进行了测定,用间接免疫溶血试验对其表达的LT-B抗原进行了测定.结果,这两种抗原在转化的细菌中均可高效表达.电镜下观察,转化的细菌在其表面形成菌毛样结构.这种转化细菌表现出猪霍乱沙门氏菌与产肠毒素性大肠杆菌的两种抗原特性,为这种双价工程菌苗的研制提供了有价值的候选菌株.本研究结果还表明,猪霍乱沙门氏菌弱毒菌苗株可作为基因转化的有效受体菌. 相似文献
133.
134.
135.
Summary Leaf cuttings without axillary buds were made from young vegetative beet plants. Roots were formed at the petiole end. Adventitious bud formation occurred at a very low frequency and could not be stimulated by application of growth regulators. Leaf cuttings with axillary buds formed plants at a higher frequency but development of buds into shoots was slow and irregular. As no vascular connections were found between petiole and axillary bud, the slow growth of the buds was attributed to insufficient supply of assimilates from the leaves. Axillary buds rapidly developed into shoots when petiole explants with buds were placed on culture media. Nearly all cultures, however, were contaminated with bacteria that originated from the inner tissue of the explants. 相似文献
136.
人体的结肠微生物区对健康有着极大的影响。自从引入益生菌和益生元的概念后,对人体肠微生物区组成的观点产生了极大的变化,详细研究复杂的细菌群落一直是个巨大的挑战。用抽样法研究肠微生物群将会更加成熟,并广泛应用于此项研究中。目前,以核酸为基础的分析方法是研究肠微生物区系的基本工具。应用先进的分子技术,使点查和鉴定结肠细菌的种类以及族系级别成为可能。目前正在对第二代益生元的概念展开广泛研究。了解内脏生态系统的作用机制以及处于内脏生态系统中的细菌的作用机制,对于益生菌和益生元将来的发展极为重要。 相似文献
137.
Inheritance of bacterial wilt resistance in tetraploid potato was investigated in segregating progenies of parent clones with resistance derived from different specific sources and different types of adaptation. A race 1 and a race 3 isolate of Pseudomonas solanacearum were used to test the resistance under warm temperatures. Results obtained indicated partial dominance of resistance. Significant general and specific combining abilities showed that both additive and non-additive gene actions are important in conditioning resistance expression. There was evidence that epistasis is an important component of the non-additive gene action in the inheritance of resistance. Other aspects of the resistance and implications for breeding are discussed. 相似文献
138.
Pyramiding of Xa7 and Xa21 for the improvement of disease resistance to bacterial blight in hybrid rice 总被引:3,自引:0,他引:3
‘Minghui 63’ is a restorer line widely used in hybrid rice production in China for the last two decades. This line and its derived hybrids, including ‘Shanyou 63’, are susceptible to bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo). To improve the bacterial blight resistance of hybrid rice, two resistance genes Xa21 and Xa7, have been introgressed into ‘Minghui 63’ by marker‐assisted selection and conventional backcrossing, respectively. The single resistance gene‐introgressed lines, Minghui 63 (Xa21) and Minghui 63 (Xa7) had higher levels of resistance to bacterial blight than their derived hybrids, Shanyou 63 (Xa21) or Shanyou 63 (Xa7). Both Xa21 and Xa7 showed incomplete dominance in the heterozygous background of rice hybrids by infection with GX325 and KS‐1‐21. The improved restorer lines, with the homozygous genotypes, Xa21Xa21 or Xa7Xa7, were more resistant than their hybrids with the heterozygous genotypes Xa21xa21 or Xa7xa7. To further enhance the bacterial blight resistance of ‘Minghui 63’ and its hybrids, Xa21 and Xa7 were pyramided into the same background using molecular marker‐aided selection. The restorer lines developed with the resistance genes Xa21 and Xa7, and their derived hybrids were evaluated for resistance after inoculation with 10 isolates of pathogens from China, Japan and the Philippines, and showed a higher level of resistance to BB than the restorer lines and derived hybrids having only one of the resistance genes. The pyramided double resistance lines and their derived hybrids have the same high level of resistance to BB. These results clearly indicate that pyramiding of dominant genes is a useful approach for improving BB resistance in hybrid rice. 相似文献
139.
Summary Soybean germplasm was screened for resistance to bacterial pustule disease. The etiological agent, Xanthomonas campestris pv. glycines, was isolated from the leaves of field grown soybean in Maharashtra, India. The screening of soybean stocks was carried out by excised leaf inoculation method. A differential susceptibility to the pathogen was observed in the tested stocks. Two stocks P-4-2 and P-169-3 were found to be completely resistant to the pathogen and displayed an incompatible reaction. Four cultivars, EC-34160, Bragg, Kalitur and PK-472 displayed moderate resistance and the remaining stocks were susceptible to the attack of the pathogen. The stocks P-4-2 and P-169-3 remained resistant even to a high concentration of 109 colony forming units (cfu)/ml of the pathogen. 相似文献
140.
Summary Phenotypic stability of bacterial leaf spot resistance in peach (Prunus persica (L.) Batsch) regenerants, either selected at the cellular level for insensitivity to a toxic culture filtrate of Xanthomonas campestris pv. pruni or screened at the whole plant level for resistance to X. campestris pv. pruni, was investigated. A detached-leaf bioassay was used to evaluate the original regenerants again after three years in the greenhouse and also after a two to three year cycle of tissue culture propagation. Peach trees derived through micropropagation from the original regenerants were also evaluated after one to three years growth in the field. Although leaf spot resistance was retained in some regenerants over time in the greenhouse, following in vitro propagation, and under field conditions, resistance was either lost or not expressed in others. Regenerants # 19-1 and #156-6, derived from embryo callus of bacterial spot susceptible Sunhigh, were significantly more resistant than Sunhigh. High levels of resistance were exhibited in greenhouse plants and field-grown trees of regenerant #122-1, derived from embryo callus of moderately resistant Redhaven. This research provides additional evidence that selecting or screening for somaclonal variants with disease resistance is a feasible approach to obtaining peach trees with increased levels of bacterial spot resistance.Abbreviations TC
Tissue-Cultured
- TF
Toxic culture Filtrate 相似文献